A feedstock containing 50 wt % SRC-I In creosote oil was hydrotreated with NI-Mo/AI203 catalysts to determine the effects of catalyst properties on the extent of hydrogenation, desulfurization, denitrogenation, and conversion of the +728 K fraction of the feed. Higher metals loadings resulted in Improved hydrogenation, whereas both higher metals loadings and larger pores enhanced denitrogenation. Catalysts with larger pores and higher metals loadings appeared to enhance the conversion of the +728 K fraction of the feedstock. All catalysts suffered large reductions in surface area, pore volume, and pore diameter, with most of this occurring during the first 50 h of processing. Percentagewise, blmodal catalysts lost less surface area and pore volume and accumulated more coke and metals than unimodal catalysts. The unlmodal catalysts were capable of being restored to their original state upon regeneration while the blmodal catalysts suffered a small loss of surface area and pore volume and had higher pellet densities.
Catalyst deactivation is a major problem in coal liquefaction processes that utilize supported-metal catalysts, such as the H-Coal process. The effect of catalyst diameter on the rate of deactivation was investigated. Data for various catalysts were obtained to validate the predictions of a theoretical model that larger diameter catalysts reduce the poisoning rate and, depending upon the extent to which the catalyst is allowed to deactivate, may allow more reactant to be processed per unit weight of catalyst. A major component of catalyst deactivation was found to be the deposition of metals on the catalyst surface. Larger diameter catalysts accumulated metals at a slower rate than smaller diameter ones. This ohenomenon is attributed to the increased diffusional resistance of the larger diameter catalyst.
The effects of pressure up to 50 kbar and of compositional changes on the absorption spectra of a number of chromium-containing silicate, phosphate, and borate glasses were observed. The spectra were analyzed into their component bands, and ligand-field theory was used to interpret the results to obtain information about the local symmetry, distortion, and local compressibility of the chromium sites. The absorption properties are explained by assuming that, on the average, the trivalent chromium ions are surrounded by six oxygen ions in an octahedral arrangement. The behavior of the spectra indicates that a random distribution of Cr–O distances about an average Cr–O distance exists and that only small disortions from cubic symmetry occur. The variation of the ligand-field parameters and the compressibilities of the sites depends mainly on the number of oxygen ions per unit volume in the glass, whether the changes are induced by external pressure or by compositional changes. Those glasses with a more open oxygen packing exhibit smaller crystal-field strengths, larger compressibilities, and larger distortions from octahedral symmetry than do the more densely packed glasses. Also, the compressibilities of the chromium sites are much less than the bulk compressibilities of the glasses.
An investigation was conducted to assess the performance and deactivation characteristics of catalysts used in the hydroprocessing reactor at the Wilsonville Advanced Coal Liquefaction Test Facility. Spent catalyst samples were collected periodically from the reactor throughout three runs. The samples were characterized by various analytical techniques and subjected to a batch activity test. All catalyst samples showed similar declines in specific pore volume, specific surface area, and average pore diameter. Although the carbon concentration reaches equilibrium very quickly, the atomic hydrogen-to-carbon ratio decreased throughout the runs. The deposition of trace metals on the catalyst increased continuously throughout the runs but at a decreasing rate.
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